The automatic dispensing of liquids into containers such as cups is relatively simple as long as the container size remains constant. The sensing of liquid in the container has, in the past, been accomplished by electrical circuits utilizing probes, capacitance sensors, optical sensors, time and even weight.
When it is necessary to fill different sized containers from the same dispensing head, some method of sensing the size of the cup must be included so that overfill or underfill does not occur. This has been accomplished in the past by electromechanical means wherein the cup comes in contact with a probe that is displaced according to the cup size. By measuring the displacement of the probe, the fill valve can be controlled by time or some other means.
In prior devices, it has been necessary to position the cup rather carefully in order to avoid a malfunction. This is particularly true in a device that requires a probe to be displaced to determine cup size. Should the probe be incorrectly displaced the dispensing valve can either continue to run and thus overflow the machine, or alternatively provide a "short fill" to the cup. In either case, the recipient is inconvenienced.
Automatic dispensing of liquids is particularly important in the fast food environment since the tempo of business in such establishments is rather high. Thus to provide a liquid dispenser that will automatically fill various sized cups without attention of the operator would be particularly advantageous.